The goal of this proposal is to understand the neural mechanisms of social recognition and memory. This information will lead to a more thorough understanding of the brain, especially sensory processing by the olfactory and vomeronasal systems, higher-order perceptual and cognitive processes involved in pattern perception, recognition, similarity judgments, and the formation of multi-component representations. In addition, the research will provide a new, unique perspective on the functional neuroanatomy of memory by investigating the role of various brain loci in social memory. Understanding of the brain, and especially of social recognition and memory processes, is relevant to the understanding of many types of human disabilities due to stroke or head injury, and also to understanding the deficits caused by a variety of degenerative diseases, including Alzheimer's disease and Korsakoff's syndrome. The specific aims of the study are to use the extensive knowledge obtained about social communication in hamsters as a model system to investigate the neural mechanisms of recognition of individuals, kin, sex, and reproductive state by odors. There are four specific goals. First, the role of the hippocampal system in discrimination and recognition of individuals will be investigated using lesions and histological methods to determine the brain areas involved and Fos histochemical methods to determine particular groups of cells that are activated during recognition and memory processes. Second, the role of the medial amygdala in sex and reproductive state recognition will be investigated using the same methods. Third, the roles of the hippocampal system (including entorhinal cortex, para-hippocampal area and peri-rhinal cortex) and of the pre-frontal agranular insular cortex in higher-order processes such as multi-component representations of individuals will be examined. Fourth, the functional neuroanatomy of kin recognition will be examined, particularly the similarities and differences between recognition of kin by familiarity and recognition of kin by phenotype matching. These experiments will provide new and unique knowledge about the neural basis of social recognition and social memory that should provide a compelling complement to what is known about other types of learning and memory. They will also provide a basis for finer-grained anatomical and neurophysiological investigations of these processes that are so crucial to the lives of animals and humans.